This invention relates to electro-optical devices whose electromagnetic radiation absorption characteristics can be selectively altered by influence of a suitably controlled electric field. More particularly, the invention is concerned with an electro-optical device which has a faster switching speed and extended cycle lifetime. Still more particularly, this invention is directed to a sandwich type cell in which two layers of electrochromic material are separated by solid, semisolid or liquid ion conducting media. It particularly relates to the addition of compounds to the conducting media.
In commonly assigned, copending U.S. applications, Ser. No. 41,153, now abandoned, Ser. No. 41,154, now abandoned, and Ser. No. 41,155, now U.S. Pat. No. 3,708,220, all filed May 25, 1970, and U.S. Pat. Nos. 3,521,941 and 3,578,843, there are described electro-optical devices exhibiting a phenomenon known as persistent electrochromism wherein electromagnetic radiation absorption characteristic of a persistent electrochromic material is altered under the influence of an electric field. Such devices were employed in sandwich arrangement between two electrodes. Coloration was induced by charging the electrochromic film negative with respect to the counter-electrode, employing an external potential. The counter-electrode can be the same as the persistent electrochromic material or different.
By reversing the original polarity of the field or by applying a new field, it was also possible to cancel, erase or bleach the visible coloration.
These steps of color induction and erasure are defined as cycling.
Although the devices described in the prior applications are effective to change their electromagnetic radiation transmitting properties under the influence of an electric field, the practicality of a simple sandwiched or layered arrangement of electrodes and layer of electrochromic material is somewhat limited due to the fact that prior devices did not exhibit high speed switching capability or extended cycle lifetime.
It is therefore an object of this invention to provide an electrochromic imaging device having an improved switching speed.
A further object is to provide an electrochromic device having improved stability and extended cycle lifetime.
These and other objects of the invention will become apparent as the description thereof proceeds.
This shortcoming has been overcome in the present invention by employing additive compounds in the electrolyte.